Merge #760

760: Add new assist to remove dbg!() calls r=matklad a=vipentti

This fixes #758.

Currently we try to maintain the cursor position relative to the statement under
cursor, if the cursor is inside the dbg! macro call.

Meaning:
```rust
let foo = dbg!(some.complex<|>().expression());
```
Should turn into:
```rust
let foo = some.complex<|>().expression();
```
With the cursor staying in place.

Co-authored-by: Ville Penttinen <villem.penttinen@gmail.com>